196 bulletin: museum of comparative zoology. 



the last spermatogonia! division. Bigelow (:07, p. 371) is of the 

 opinion "that a pairing of individual chromosomes does not occur at 

 all in Gonionemus, but that synapsis occurs between the chromatic 

 microsomes; and takes place while these are intimately associated 

 in the homogeneous net" of the primary spermatocytes. A. und 

 K. E. Schreiner (:06-07) in attempting to correlate the synapsis stage 

 in all animals, have claimed that during the polar arrangement of the 

 loops, at first present in the same number as the somatic chromosomes, 

 a reduction in number to one-half takes place by a side to side conjuga- 

 tion. This is apparently not true for many animals, where an end to 

 end conjugation occurs. The polar loops were not commonly observed 

 in Tubularia, and their arrangement was not always clear. In some 

 cases the number of loops was about half, in other cases more than 

 half, the number of chromosomes in somatic cells. A reduction is thus 

 suggested as taking place during this period, though the evidence is 

 not sufficient to furnish convincing proof; and no evidence could be 

 obtained as to how the reduction occurred. 



Trinci (:07) found that after synapsis a continuous thread was 

 present in Tiarella. This segmented into chromosomes, — though he 

 does not say whether or not in a reduced number, — which anastomosed 

 into a network persisting throughout the growth period. In Phialidi- 

 um the chromosomes, formed in the same way, scatter through the 

 nucleus and lose their staining capacity, but retain their individuality 

 through the growth period. In Tubularia I find that the loops soon 

 lose their polarity, and become more delicate and distinctly granular; 

 in a few preparations threads lying side by side suggest a splitting of 

 the loops, but the evidence on this latter point is so meager that it may 

 be without significance. The chromatin in the germinative vesicle 

 of eggs in later stages of growth is always finely granular and scattered 

 along the reticulum, and all trace of the loops of the synapsis period is 

 lost. 



The formation and behavior of the chromosomes in the maturation 

 spindle I could not observe in Tubularia, and the important evidence 

 which this would oft'er in regard to reduction is therefore lacking. 

 It was possible, however, to observe these stages in Pennaria, and the 

 conditions there may help to fill the gap in the history of Tubularia. 

 In the equatorial plate of the first maturation spindle of Pennaria the 

 chromosomes were present in the reduced number. Furthermore, 

 they were partly in the form of tetrads, and in later stages in the form 

 of X- and v-shaped figures ; this suggests a splitting in the heterotypical 

 fashion, such as is common in maturation mitoses. Since in the later 



